1. Field of the Invention
The present invention relates to a photosensitive polymer and a resist composition containing the same, and more particularly, to a photosensitive polymer having a main chain consisting of only norbornene-type alicyclic units, and a resist composition containing the same.
2. Description of the Related Art
As semiconductor devices become highly integrated, fine pattern formation is required in a photolithography process. Further, a pattern size having a design rule of less than 0.2 xcexcm is required for devices beyond 1 giga capacity. Accordingly, there are limitations in using a conventional resist material with a KrF excimer laser (248 nm). Thus, a new resist material capable of being developed using an ArF excimer laser (193 nm) has been developed in a lithography process.
The resist material used in the lithography process using the ArF excimer laser has several problems in being commercially used, compared to the conventional resist materials. The most typical problems are transmittance of a polymer and resistance to dry etching.
As the widely known ArF resist materials, (meth)acrylate polymers are generally used. In particular, the most typical resist material is poly(methyl methacrylate-tert-butyl methacrylate-methacrylic acid) terpolymer system manufactured by IBM, Inc. However, such polymers have very weak resistance to dry etching.
Accordingly, to increase the resistance to dry etching, a polymer having a backbone composed of an alicyclic compound such as an isobornyl group, an adamantyl group or a tricyclodecanyl group, is used. However, the resulting resist still exhibits weak resistance to dry etching.
Alternatively, in order to increase the resistance to dry etching, norbornene-type polymers having a main chain consisting of alicyclic units are used. The norbornene-type polymers are known to be incapable of radical polymerization by themselves. In this context, norbornene-type polymers have been prepared by alternating copolymerization with maleic anhydride. However, due to the introduction of maleic anhydride, the resistance to dry etching is lowered and the stability over time is poor, shortening the shelflife of the polymer.
Accordingly, attempts to attain copolymers having a main chain consisting of only norbornene-type units have been tried using addition polymerization using a metallic catalyst such as palladium (see Joice P. Mathew et al., Macromolecules, 1996, 29(8), p 2755.). However, it is difficult to completely remove the metallic catalyst used for polymerization. Thus, in the case of using a resist composition obtained from the polymer, metallic components may remain on a wafer. These remaining metallic components impede the use of the resist in manufacturing an electronic apparatus such as a semiconductor device.
The present invention is therefore directed to photosensitive polymer which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to provide a photosensitive polymer having a main chain consisting of only norbornene-type units so that sufficient resistance to dry etching can be attained.
It is another object of the present invention to provide a resist composition which contains the photosensitive polymer, which avoids metallic components remaining on a wafer, and which provides for excellent lithographic performance during a lithography process using an ArF excimer laser.
Accordingly, to achieve the above objective, there is provided a photosensitive polymer represented by the following formula: 
wherein R1 is an acid-labile tertiary alkyl ester group, R2 is hydrogen atom, methyl, ethyl, carboxyl, xcex3-butyrolactone-2-yl ester, xcex3-butyrolactone-3-yl ester, pantolactone-2-yl ester, mevalonic lactone ester, 3-tetrahydrofuranyl ester, 2,3-propylenecarbonate-1-yl ester, 3-methyl-xcex3-butyrolactone-3-yl ester or C3 to C20 alicyclic hydrocarbon, a/(a+b+c) is 0.1xcx9c0.7, b/(a+b+c) is 0.1xcx9c0.8, c/(a+b+c) is 0.0xcx9c0.8, and n is an integer in the range of 0 to 2.
Preferably, the photosensitive polymer has a weight-average molecular weight of 1,000xcx9c100,000. Also, R1 is preferably a substituted or unsubstituted C7 to C20 alicyclic hydrocarbon compound. More preferably, R1 is 2-methyl-2-norbornyl ester, 2-ethyl-2-norbornyl ester, 2-methyl-2-isobornyl ester, 2-ethyl-2-isobornyl ester, 8-methyl-8-tricyclo[5.2.1.02.6]decyl ester, 8-ethyl-8-tricyclo[5.2.1.02.6]decyl ester, 2-methyl-2-adamantyl ester, 2-ethyl-2-adamantyl ester or 1-adamantyl-1-methylethyl ester.
According to another aspect of the present invention, there is provided a resist composition comprising (a) a photosensitive polymer represented by the following formula: 
wherein R1 is an acid-labile tertiary alkyl ester group, R2 is hydrogen atom, methyl, ethyl, carboxyl, xcex3-butyrolactone-2-yl ester, xcex3-butyrolactone-3-yl ester, pantolactone-2-yl ester, mevalonic lactone ester, 3-tetrahydrofuranyl ester, 2,3-propylenecarbonate-1-yl ester, 3-methyl-xcex3-butyrolactone-3-yl ester or C3 to C20 alicyclic hydrocarbon, a/(a+b+c) is 0.1xcx9c0.7, b/(a+b+c) is 0.1xcx9c0.8, c/(a+b+c) is 0.0xcx9c0.8, and n is an integer in the range of 0 to 2, and (b) a photoacid generator (PAG).
Preferably, the resists composition includes the PAG in an amount of 1 to 15% by weight based on the total weight of the polymer.
Examples of the PAG include triarylsulfonium salts, diaryliodonium salts, sulfonates or mixtures thereof. Preferably, the PAG is triphenylsulfonium triflate, triphenylsulfonium antimonate, diphenyliodonium triflate, diphenyliodonium antimonate, methoxydiphenyliodonium triflate, di-t-butyl diphenyliodonium triflate, 2,6-dinitrobenzyl sulfonates, pyrogallol tris(alkylsulfonates), N-hydroxysuccinimide triflate, norbornene-dicarboximide triflate, triphenylsulfonium nonaflate, diphenyliodonium nonaflate, methoxydiphenyliodonium nonaflate, di-t-butyldiphenyliodonium nonaflate, N-hydroxysuccinimide nonaflate, norbornene-dicarboximide nonaflate, triphenylsulfonium perfluorooctanesulfonate (PFOS), diphenyliodonium PFOS, methoxy diphenyliodonium PFOS, di-t-butyl diphenyliodonium triflate, N-hydroxysuccinimide PFOS, norbornene-dicarboximide PFOS, or a mixture thereof.
The resist composition of the present invention may further include an organic base. Preferably, the resist composition includes the organic base in an amount of 0.01 to 2.0% by weight based on the total weight of the polymer. Usable organic bases include triethylamine, triisobutylamine, triisooctylamine, diethanolamine, triethanolamine or a mixture thereof. Also, the resist composition of the present invention may further include a surfactant, preferably in an amount of 30 to 200 ppm.
The photosensitive polymer according to the present invention has a main chain consisting of only norbornene-type units so that sufficient resistance to dry etching can be attained. The photosensitive polymer having such a structure can be prepared with a high yield without using a metallic catalyst. Also, the resist composition obtained from the polymer exhibits excellent adhesion.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
A photosensitive polymer according to the present invention is represented by the following formula (1): 
wherein R1 is a group which can be deprotected from the main chain of the polymer by the action of acid generated during exposure, serves to enhance the resistance to dry etching and serves as a dissolution inhibitor. R1 is a bulky tertiary alkyl ester group having a substituted or unsubstituted C7 to C20 alicyclic hydrocarbon compound, and examples thereof include 2-methyl-2-norbornyl ester, 2-ethyl-2-norbornyl ester, 2-methyl-2-isobornyl ester, 2-ethyl-2-isobornyl ester, 8-methyl-8-tricyclo[5.2.1.02.6]decyl ester, 8-ethyl-8-tricyclo[5.2.1.02.6]decyl ester, 2-methyl-2-adamantyl ester, 2-ethyl-2-adamantyl ester and 1-adamantyl-1-methylethyl ester.
R2 is a polar group induced as an adhesion promoter for improving adhesion characteristics in the polymer, and examples thereof include hydrogen atom, methyl, ethyl, carboxyl, xcex3-butyrolactone-2-yl ester, xcex3-butyrolactone-3-yl ester, pantolactone-2-yl ester, mevalonic lactone ester, 3-tetrahydrofuranyl ester, 2,3-propylenecarbonate-1-yl ester, 3-methyl-xcex3-butyrolactone-3-yl ester and C3 to C20 alicyclic hydrocarbon.
The anhydride represented in the unit of a second monomer in Formula (1) increases the dry etching resistance of the photosensitive polymer, improves wettability and serves as an adhesion promoter.
In Formula (1), a/(a+b+c) is 0.1xcx9c0.7, b/(a+b+c) is 0.1xcx9c0.8, c/(a+b+c) is 0.0xcx9c0.8 n is an integer in the range of 0 to 2.
The photosensitive polymer represented by Formula (1) has all characteristics necessary for serving as a resist for deep UV. Copolymerization of the photosensitive polymers cannot be achieved by conventional radical polymerization or addition polymerization using a metallic catalyst. Even though polymerization is achieved, the molecular weight of the obtained polymer is very low, that is, about several hundreds, and the yield is very low.
Polymerization methods of a photosensitive polymer according to preferred embodiments of the present invention will now be described in detail.